The invention relates generally to continuous casting.
More particularly, the invention relates to an electromagnetic stirrer for stirring the molten core of a partially solidified, continuously cast strand in a continuous casting apparatus.
Electromagnetic stirrers for continuous casting apparatus are known and generally include a casing which accommodates electromagnetic coils provided with respective cores. Such a stirrer is cooled by a cooling liquid. Electromagnetic stirrers are used both inside and beneath continuous casting molds and the purpose of these stirrers is to improve the quality of a continuously cast strand.
The French Patent Application No. 78 33156 discloses an electromagnetic stirrer which functions to stir the molten core of a partially solidified, continuously cast strand and is disposed inside a continuous casting mold. The stirrer comprises electromagnetic coils provided with respective cores and a magnetic yoke. The coils, cores and yoke are accommodated in a casing having an inlet and an outlet for cooling water. The cooling water, which is used to remove the heat generated by the coils, is the same water as used to cool the mold.
Although the hardness, salt content and pH of the mold cooling water, as well as the amount of suspended matter, are kept within narrow ranges, flow of the cooling water through the electromagnetic stirrer, and the accompanying exposure of the cooling water to magnetic fields, may result in harmful sedimentation and other deposition. This not only requires costly downtime for additional maintenance but can also lead to malfunctions.
Expensive supplemental water treatment is necessary in order to avoid such malfunctions and additional maintenance. Thus, the water must be purified to such a degree that the specific conductivity does not exceed 500 microsiemens per centimeter and the maximum particle size of suspended matter is no greater than 5 microns. Moreover, all ferromagnetic particles must be filtered out and the concentrations of carbon dioxide, ammonia, nitrides, dissolved iron, dissolved manganese, sulfates, chlorides and silicates must be minimized.
The additional maintenance, malfunctions and supplementary water treatment outlined above all reduce the economic benefits and efficiency of electromagnetic stirring during continuous casting.